diff --git a/src/frontend/numparam/xpressn.c b/src/frontend/numparam/xpressn.c
index a1b274216..0662778d5 100644
--- a/src/frontend/numparam/xpressn.c
+++ b/src/frontend/numparam/xpressn.c
@@ -556,9 +556,9 @@ findsubckt(dico_t *dico, const char * const s)
 
     spice_dstring_init(&ustr);
 
-    k_ptr--;
-    while ((k_ptr >= s) && (*k_ptr <= ' '))
+    while ((k_ptr - 1 >= s) && (*(k_ptr-1) <= ' '))
         k_ptr--;
+    k_ptr--;
 
     j_ptr = k_ptr;